The present invention relates to a silicon carbide sintered body which is useful as a semiconductor fabrication equipment part, an electronic information equipment part, or a structural part of vacuum equipment or the like, which has high density and conductivity, and which is processable by electrical discharge machining, and to a fabrication method thereof.
Hitherto, silicon carbide has been noted as a material to be used in high temperature regions because of its excellent strength, heat resistance, thermal impact resistance and wear resistance at high temperatures exceeding 1000xc2x0 C. Recently, the same has been used as a substitute material for quartz in semiconductor fabrication devices.
One method of fabricating a sintered body made of such silicon carbide is a reaction sintering method. In this reaction sintering method, first, silicon carbide powder and an organic material composed of carbon source or carbon powder are dissolved or dispersed in a solvent, and a mixed powder slurry is fabricated. Then the obtained mixed powder is poured into a mold, extrusion forming die or press forming die, and dried to obtain a green body. Then the obtained green body is heated in a vacuum atmosphere or inert gas atmosphere, and immersed in molten metallic silicon. Free carbon in the green body and silicon sucked up into the green body by capillary action react, so that the silicon carbide sintered body is obtained.
However, the silicon carbide sintered body fabricated as above is generally electrically insulative. Hence, electrical discharge machining could not be performed, and there were limits in machining. In particular, when manufacturing a thin film part of 1 mm or less, handling of the green body was difficult. Therefore, it was usually necessary to manufacture a green body of several millimeters and, after forming a sintered body, grind-process the same to a specified thickness by milling machining or the like, which was a significant economical drawback.
An object of the present invention is to provide a silicon carbide sintered body having high density and conductivity, which is electrical discharge machinable, and a fabrication method thereof.
The present inventors studied intensively, thus finding that a silicon carbide sintered body meeting this object can be fabricated, and completed the present invention.
That is, the present invention provides, by reaction sintering, a silicon carbide sintered body having a density of 2.90 g/cm3 or more and a volume resistivity of 100 xcexa9xc2x7cm or less, and containing nitrogen at 150 ppm or more.
The present invention further provides a fabrication method of the silicon carbide sintered body, including: a step of fabricating a mixed powder slurry by dissolving or dispersing silicon carbide powder, at least one organic material composed of a nitrogen source, and at least one organic material composed of a carbon source or carbon powder in a solvent; a step of fabricating a green body by pouring the mixed powder slurry into a mold and drying; and a step of filling pores in the green body by immersing the green body in high purity metallic silicon that has been heated to 1450 to 1700xc2x0 C. and melted in a vacuum atmosphere or inert gas atmosphere, and generating silicon carbide by reacting silicon sucked up into the pores in the green body by capillary action with free carbon in the green body.
Further, the present invention provides a fabrication method of a silicon carbide sintered body, including: a step of fabricating a silicon carbide powder containing nitrogen by dissolving at least one silicon source containing a silicon compound, at least one carbon source containing a organic compound that generates carbon when heated, at least one organic material composed of a nitrogen source, and a polymerizing or crosslinking catalyst in a solvent, drying, and then burning an obtained powder in a non-oxidizing atmosphere; a step of fabricating a mixed powder slurry by dissolving or dispersing the silicon carbide powder containing nitrogen and at least one organic material composed of a carbon source or carbon powder in a solvent; a step of fabricating a green body by pouring the mixed powder slurry into a mold and drying; and a step of filling pores in the green body by immersing the green body in high purity silicon that has been heated to 1450 to 1700xc2x0 C. in a vacuum atmosphere or inert gas atmosphere and melted, and generating silicon carbide by reacting silicon sucked up into the pores in the green body by capillary action with free carbon in the green body.